


Wet Weather Warning

by la_muerta



Series: For Science! [2]
Category: Shadowhunters (TV)
Genre: Alternate Universe - Human, Alternate Universe - Space, Barebacking, Consentacles, Dom/sub Undertones, Fluff, Fluff and Smut, For Science!, Knotting, M/M, Mad Science, Multiple Orgasms, Non-Traditional Alpha/Beta/Omega Dynamics, Overstimulation, Plot What Plot/Porn Without Plot, Porn with Feelings, Self-Bondage, Shameless Smut, Tentacle Sex, Tentacletober Day 18: In Space
Language: English
Status: Completed
Published: 2019-10-18
Updated: 2019-10-18
Packaged: 2020-12-22 16:15:01
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,686
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/21079667
Author URL: https://archiveofourown.org/users/la_muerta/pseuds/la_muerta
Summary: Alec finally tries to ask Magnus out on a date when they land on an alien planet that seems like the ultimate intergalactic beach holiday destination. Unfortunately, Magnus claims to have developed an allergy to... water?





	Wet Weather Warning

**Author's Note:**

  * For [lynne_monstr](https://archiveofourown.org/users/lynne_monstr/gifts).

> This is a sequel to [Heat Wave](https://archiveofourown.org/works/14505903), so it'll make more sense if you read part one first ;)
> 
> Gifted to [lynne_monstr](https://archiveofourown.org/users/lynne_monstr) because without your fabulous Tentacletober event, this draft would probably have been sitting half-written in my computer for another year lol

"Captain? Captain?!" 

"Huh?" Alec snapped out of his daydream to find Simon's face a couple of inches away from his own and jerked backwards in surprise. "What the fuck?" 

"I've been trying to get your attention for ten minutes," Simon said huffily. 

"If you want to fantasise about Magnus, go do it in your room," Jace chimed in from his own station. "The bridge is for serious business."

"You do know that I can see you playing Galaga on your screen, right?" Alec said dryly. 

"I'm practicing shooting down hostile alien forces," Jace corrected him. 

"Great job, Jace, except this ship has no weaponry," Alec replied, rolling his eyes. "Um, you wanted to ask me something?" he asked Simon. 

"There's an uncharted planet showing up on the radar, with no signs of intelligent life. Should we attempt a landing?" Simon asked. 

"Yes, but could you do a more thorough scan for all lifeforms, intelligent or not?" Alec asked. He'd learnt the hard way (pun not intended) not to trust Simon's damned scanner. "To be honest, I don't think Jace would show up if you tried to scan for intelligent life." 

Jace spared five seconds away from navigating his little pixellated spaceship to give Alec the finger. 

"Hey, if it's safe, maybe you should bring Magnus with you on your reconnaissance mission. Like a date," Simon suggested. "I mean, you clearly enjoy each other's company."

"A lot. Very loudly," Jace contributed. 

Alec narrowed his eyes at Jace. "Mind your own business." 

"I wish I could, bro. But this ship is very small, and the walls are a lot thinner than you think they are. It's been two weeks since that thing with the alien breeding ritual darts, and you guys have just been avoiding each other. Everyone on this ship is going to spontaneously combust from the unresolved sexual tension, ok?" Jace complained. 

"I don't know about 'unresolved'," Maia muttered from her co-pilot seat. "But yes, for the sake of the sanity of your crew, please go and ask Magnus out, so we won't have to deal with the two of you moping around like idiots." 

"All clear, Captain!" Simon reported cheerfully. 

"Great! Now get your ass down to the med bay, I'll handle the landing," Maia said, dragging Alec out of his chair and pushing him out of the bridge. 

\--

Alec _hadn't_ been avoiding Magnus. He was just the kind of person who wouldn't go to the med bay voluntarily unless it was a life-or-death situation, that's all. On the other hand, he was sure Magnus was avoiding him - he hardly saw him any more, because it seemed like Magnus was practically living in the med bay these days. They didn't have fixed mealtimes on the ship, with everyone just sort of going to the food dispenser in the kitchen and eating whenever they remembered, but there was a food dispenser in the med bay as well, so Magnus didn't even have to come out for food.

Alec hadn't been avoiding Magnus, but to be honest, if he bumped into Magnus in the hallways, he wouldn't know what to say. The effects of the aphrodisiac they'd been tagged with had lasted three days, and they had basically spent all that time having sex - a lot of alien-hormone-driven sex with their new alien-hormone modified genitals. The fact was, those three days of sex with Magnus had ruined Alec for sex with anyone else, ever again. Alec had never thought of himself as a size queen, but the burn of the stretch just before Magnus' knot slipped into his body, and the way it felt inside him, filling him up completely, had been really fucking _incredible_. There was also something deliciously filthy about being forced to take load after load of Magnus' come inside his body, to have all that come sealed inside until Magnus' knot finally went down enough for them to separate and it flowed down his thighs with no way for him to stop it. With his sense of smell magnified by the weird alien drugs they'd been injected with, the scent of Magnus so blatantly on him, _in_ him, had made Alec feel thoroughly owned, in a good way. But on the other hand, having Magnus writhing under him, legs spread wide and cock leaking, both hands pinching his own nipples while he begged Alec to _knot me, please, stretch me open with your knot _was something else, and Alec really had to stop thinking about it before he popped an inconvenient boner in the corridor. 

But the point was, what did you say to someone whom you'd had more than thirty rounds of sex with, but still hadn't even gone on a date with? There was also that tiny problem, where after the alien heat had subsided, both of them had come to realise that the changes that had been made to their bodies were permanent, and it was entirely Alec's fault that Magnus was now stuck with freaky alien genitalia and a leaky ass.

He was at the door of the med bay, hand already lifted to knock, when he started to have second thoughts. As dating spots went, maybe an unknown alien planet wasn't the best choice. For all Alec knew, it could be filled with venomous creatures and carnivorous plants, or Simon's stupid scanner had malfunctioned again and the natives might eat them, or-

"Alexander!" 

Magnus looked just as surprised to see him there as Alec was to have the door suddenly slide open. He gawked at Magnus for a few seconds before he remembered to drop his hand. 

"Hey, um, what's up?" Alec said, then immediately wanted to kick himself. 

"I'm sorry, Alexander, I promise I haven't been avoiding you," Magnus said, fiddling with the silver cuff on his ear. "I've just been very distracted lately. I've been trying to develop a cure for the lingering physical symptoms of the alien aphrodisiac. Unfortunately, I haven't had much luck so far, but I will keep you updated on the progress of my experiments, of course." 

"Oh. Ok, yeah," Alec mumbled. 

"I was just about to head up to the bridge to ask why we're slowing down," Magnus said.

"We're landing on the planet up ahead. I came to ask you if you wanted to go off the ship with me," Alec got out in a rush. 

"Of course!" Magnus replied immediately, but Alec’s relief and euphoria that Magnus had understood his intentions were short-lived. "It's part of protocol to bring a science officer and I know Izzy is down with a case of cold sores. It would be terrible if she passed the herpes simplex virus on to an unsuspecting planet. I will be ready to go in five minutes."

"Right. See you in five," Alec replied. 

He managed to make it all the way round the corner, out of Magnus' sight, before banging his head repeatedly on the wall in frustration. 

\--

Their reconnaissance mission started well enough. Maia landed their ship on a plateau of sorts, and everyone was annoyingly cheery while they waved goodbye to Alec and Magnus. From what they had seen, the surface of the planet seemed to be split pretty evenly between ocean and desert - red hills tapering to wide sandy stretches of arid, barren land which then vanished into freshwater oceans so blue they looked like someone had poured a million gallons of food colouring into it. 

Magnus had suggested that they explore the dry land first, and Alec had figured that they would be done with that really quickly because they were no plants and no animals in sight. But after Magnus had taken soil samples from a few spots, he started talking about climbing _another_ identical hill to take a sample of the soil there as well instead of moving on to explore the water. 

"Magnus, do you have a fear of water or something like that?" Alec asked, realisation dawning. 

"No, not at all," Magnus said a little too quickly. "I'm just having a bit of an, um, allergic reaction to something, and water seems to make it worse. But we're not planning to go too deep into the water, so I'm sure I'll be fine."

Still, when they got to the water's edge, Alec told Magnus to hang back. Their landing gear was designed to be amphibious, and although they had left off the helmets and oxygen tanks because the ship's computer had indicated that the alien planet's atmosphere was not hazardous to humans, they could always activate the swim fins and inflate the in-built floatation pockets in their gear, so drowning wasn't really a worry. Despite the alarming shade of blue, a preliminary toxicity reading on the water came back clear. Alec waded out until he was thigh-deep in the gentle waves, shielding his eyes as he tried to look further out - there were a few small rocky islands, but that was about it. 

It was a nice place - quiet, clean, peaceful. Stick a beach umbrella in the sand, and this could be the ultimate intergalactic beach holiday destination. There were some dark clouds gathering in the distance, but it was nothing to worry about. The little device he held in his hand was currently analysing the water sample he'd scooped up for microorganisms, and once it was done they could go back to the ship. In fact, maybe they could stay on this planet for a little while so the crew could stretch their legs and play beach volleyball or something, and Alec could psyche himself up for another attempt at asking Magnus out on a date. 

He was just wondering if the ship's food dispenser could be persuaded to make anything resembling a cocktail when his communicator went off. 

"Simon?" 

"_Captain, there's a storm approaching your coordinates_." 

"I don't think there're any signs of life on this planet - no microbes," Alec said. "We'll be on our way back to the ship before the storm hits."

"_Don't be in a hurry to get back. Go spend as much time as you want with Magnus_," Jace's voice came over the communicator, as if Magnus wasn't right there, close enough to overhear. 

"Fuck off," Alec muttered and cut the call. He glanced back to the shore, where Magnus was watching the approaching storm clouds with apprehension. "Almost done!" he called back, indicating the scanner. "It's already at-" 

Alec took a step backwards to maintain his balance in the shifting sand and let out a yelp of surprise when he accidentally stepped right into a powerful rip current that swept him off his feet. He fell into the water with a gigantic splash, sputtering and flailing his arms like a pinwheel, but the current was strong and dragged him out to sea in an instant. He swallowed a mouthful of water instead of air and started choking, too surprised to activate the floats in his gear. By the time he'd regained his bearings enough to try to get to the surface, he was a few metres underwater and still being dragged by the current. He kicked out with all his might, activating his swim fins and floats, but none of them seemed to be any use. He'd lost his communicator and scanner and his lungs were burning, and he thought he'd hit his head at some point because he could see Magnus swimming towards him with incredible speed, but for some reason Magnus was being pursued by half a dozen pink sea snakes. 

Alec felt Magnus' strong arms surround him and wrapped his own arms around Magnus instinctively. Magnus surged upwards and when they finally broke through the surface, Alec gasped with relief as sweet oxygen filled his lungs. He relaxed into Magnus' arms and leaned his head on his shoulder, letting Magnus carry him to one of the rocky islands he had spotted earlier. In the time that Alec had been fighting with the current, the storm had found them, fat drops of rain smacking the surface of the ocean and pelting them hard enough that Alec flinched, but thankfully there was a cave for them to take shelter in on the island Magnus had picked.

Alec had recovered enough to try to pull himself onto the island, but it was only when he tried to give Magnus a hand up that he spotted one of the sea snakes trailing behind Magnus. He tried to make a grab for it and fling it back into the water, but it recoiled from him and _Magnus_ recoiled from him, going back into the water.

"Magnus, what are you doing?" Alec asked worriedly. The once calm ocean was getting very choppy now as the storm picked up around them. He reached out for Magnus again, but Magnus shook his head.

"Maybe I should just stay in the water," Magnus said, already struggling to stay close to the island as the waves buffeted him.

"The water isn't safe and the storm may get worse, get in here," Alec huffed.

Magnus hesitated, then allowed Alec to pull him out of the water. Alec spotted the long pink things behind Magnus but elected not to mention them until he had gotten Magnus safely inside the cave. Besides, they seemed to be trying to hide from him behind Magnus' broad frame.

After a few minutes of tense silence, Alec could bear it no longer. "Magnus, what are those things?" he blurted out.

Magnus sighed and turned around to show Alec his back. There were six flesh-coloured appendages peeking out from under Magnus' shirt on his lower back, coiled up and attempting unsuccessfully to shrink upon themselves. 

Magnus had _tentacles_.

"Remember that I told you I was trying to develop a cure for the alien aphrodisiac?" Magnus said a little sheepishly. "I've been testing them out on myself, and unfortunately there have been some... unexpected side effects."

\--

"So are these tentacles permanent? Like the..." Alec gestured vaguely at his groin. 

"I don't know," Magnus admitted. "I started out with small doses, and they did cure the physical symptoms temporarily. Every time I upped the dosage, the effects lasted a little longer, and I'm afraid I got a bit impatient and used too large a dose this time." 

"Oh. So does that mean that you no longer have the rest of the stuff?" Alec asked in surprise. He had to admit that he was a little disappointed when Magnus nodded. 

"I'm not sure I prefer the tentacles. I think the other symptoms were much easier to manage, even if the tentacles only grow out when I come into contact with water," Magnus said gloomily. "Most of the time these things seem to have a mind of their own - which I suppose shouldn't come as a surprise since cephalopod arms can make decisions independent of the central nervous system. Or maybe I'm just really bad at coordinating them, and sometimes they just freeze up if I think too hard."

"If you didn't have them, I'd probably have drowned," Alec pointed out. "At least tentacles are useful for something. I'm just going to be a turn-off in bed." 

"I'd disagree. I think having a self-lubricating ass and an extra thick cock would make you _very_ popular in bed," Magnus joked, then added quietly, "If anyone is going to be a turn-off in bed, it's probably me."

"No, you aren't," Alec said quickly.

"You don't have to lie to me to spare my feelings, Alexander," Magnus scoffed.

"Magnus, I don't care if you grow a tail or you turn yourself bright blue, because that doesn't change who you _are_," Alec insisted. He scooted a little closer to Magnus. "Is that why you've been avoiding me? Anyway the alien stuff was my fault in the first place."

"Getting drugged by aliens wasn't _your_ fault," Magnus protested. 

Then Alec felt something touch his hand, and he looked down to see one of Magnus' tentacles trying to curl its tip around his little finger. He froze and Magnus turned to see what he was looking at.

"Shit! Sorry," Magnus said, hurriedly grabbing the tentacle and pulling it away. "Like I said, it's like they have a mind of their own sometimes."

"No, it's ok," Alec said, and on a hunch he took one of Magnus' hands firmly in his own, lacing their fingers together. "Maybe it was just hinting to me that I ought to have done this sooner."

Magnus smiled in relief and squeezed his hand, then noticed that one tentacle had coiled itself around Alec's wrist and he huffed in exasperation. "For goodness' sake-"

"I think they're kinda cute," Alec said.

"_Cute?_" Magnus repeated incredulously.

Another tentacle had landed on Alec's shoulder, and he let it curl around the index finger of his free hand. Magnus watched wide-eyed as Alec examined it. It was about the width of two fingers, covered in smooth, ordinary-looking skin - like a very long, flexible finger that was all muscle and no bone. Alec smoothed a thumb over it and brought it to his lips to kiss it the way he would the back of a hand. 

Magnus breathed in sharply. "Oh."

"I'm sorry, did that hurt?" Alec asked in confusion.

"No, it's just..." Magnus squirmed. "Maybe the effects of the cure are wearing off."

"How can you tell?"

"It seems that the tentacles are more sensitive than I realised," Magnus said, voice strained, then Alec realised that he'd been rubbing his thumb over the tentacle in his hand in what had been intended as a soothing gesture.

"Oh. Do you want me to stop?" Alec asked. Now that he'd realised what was going on, he could sense the shift in the enclosed space of the cave, the very familiar musk of Magnus' arousal like a sweet undertone in counterpoint to the clean smell of rain outside. 

"Is it terrible of me if I say I don't want you to stop?" Magnus asked with a slightly breathless laugh. "I wonder if the cure will wear off faster if I flood my system with the hormones that encourage the return of the original symptoms."

Certain parts of Alec's anatomy were immediately onboard with the idea. He cleared his throat. "We should test out that hypothesis. That's like, the scientific method, right?" 

Magnus' lips quirked up in a smile. "As your head science officer and a big proponent of the scientific method, I wouldn't be opposed to your suggestion, Captain."

Alec grinned and kissed the tentacle again, peppering gentle kisses all the way down from somewhere in the middle to the tip. Then, with his eyes on Magnus', he sucked the tip of the tentacle into his mouth, letting it slide out slowly. Magnus moaned and surged forward to kiss him hard on the lips, and all at once there were tentacles everywhere - wrapping themselves around Alec's shoulders, wrist, and waist, very boldly going straight to caress Alec's cock through his pants, and one was attempting to squeeze his ass. Alec made a muffled sound of surprise and Magnus backed off immediately. 

"Sorry."

"I don't mind," Alec said, pulling Magnus close again, tentacles and all. 

Getting out of their clothes proved to be a very complicated affair with all the extra limbs getting in the way, especially since Magnus was having a hard time controlling them and they all just seemed to want to cling to Alec. Alec was sitting cross-legged and Magnus was in his lap, their shirts already off, and when one particularly tenacious tentacle coiled around Alec's wrist made it impossible for Alec to undo Magnus' fly, Alec moved it to his mouth and sucked on it to distract it, and moaned when the tentacle pressed deeper into his mouth. Another tentacle found its way into his mouth, and he panted around them as Magnus finally got his own fly open and started working on Alec's. He wrapped his hands around their cocks and stroked them together as Alec reached behind into Magnus' pants to tease his entrance. Magnus was just slick enough for Alec to push two fingers inside him.

"Ah! Fuck, Alexander," Magnus cried out, his voice too loud in the enclosed space. 

Alec took one of Magnus' tentacles out of his mouth and pressed it to Magnus' own lips, then guided the second one into Magnus' mouth as well. Magnus' eyes went wide but he didn't fight it, grinding down on Alec's fingers. 

Alec slid his fingers out and cupped the back of Magnus' neck, licking into his mouth and around the tentacles as his hands caught two more of Magnus' tentacles. He pinned Magnus' arms behind his back and coiled the tentacles around them, binding Magnus' arms, then gently lowered Magnus to the floor so that he could take off their pants properly. As Alec moved between Magnus' legs, the last two tentacles wrapped around Magnus' thighs and ankles of their own accord, holding Magnus spread for him. 

"Fuck, you're gorgeous," Alec murmured, taking in the sight of Magnus with his arms and legs bound by his tentacles and his lips stretched around the tentacles gagging him.

Alec took Magnus' cock into his mouth, revelling in the taste of his precome blooming on his tongue, then let go of it with an obscene pop, making Magnus groan. Alec kissed his way up Magnus' body, taking time to tease Magnus' nipples with his teeth and tongue, and sucking very light bruises from Magnus' collar to his jawline, and when he was finally face to face with Magnus, he carefully eased the tentacles out of his mouth so he could press his lips to Magnus' in a slow, sweet kiss. 

"Ready for me?" he asked, taking his cock in hand and rubbing the head of it against Magnus' entrance, spreading the slick all around. 

Magnus gasped and strained to push himself onto Alec's cock even with his limited range of movement. "Alexander, _please_."

Alec held his cock more firmly and pressed it into Magnus, claiming Magnus' lips again to swallow his moans as Alec's cock filled him in one long, slow movement. Their tongues slid against each other's in heated open-mouthed kisses as Alec gave Magnus some time to adjust, then Alec pulled out of Magnus almost all the way before thrusting back in. Magnus keened as Alec repeated the motion again, his body hot and tight around Alec's cock. With his arms bound behind his back, his two free tentacles seemed to move in lieu of his arms - one wrapped itself around Alec to hold him close and another began to stroke Alec's back, wandering further and further down until it reached Alec's ass. 

Alec could feel the tip of the tentacle flicking against his entrance like a tongue, covering itself in the natural lubrication that was seeping out of his ass, then moaned when the tentacle slipped right into him. The second one moved down to join the first, and although Magnus didn't have enough control over his tentacles to fuck Alec with them, they were buried so deep inside Alec that every time he pulled his cock out of Magnus he was fucking himself right onto Magnus' tentacles. 

"Fuck, Magnus, push them deeper into me," Alec panted, arching his back in pleasure when Magnus complied. He was close - he could feel his knot swelling and starting to catch on Magnus' rim every time he fucked into him. 

Holding Magnus close to him, Alec turned them around so that Magnus was on top, gravity dragging him down onto Alec's cock and the knot at the base of it. Alec gripped Magnus' hips firmly and began to fuck upwards in quick, hard thrusts. Magnus gasped Alec's name in pleasure, his own dick bobbing hard and neglected against his abs. 

"C'mon, Magnus. Let me see you take my knot," Alec murmured. 

Magnus closed his eyes, mouth falling open as he he bore down. Alec could feel Magnus' body struggling to accommodate the thick base of his cock, _see_ Magnus' tight rim being stretched around it, and in a moment the knot breached Magnus' body completely and Alec slammed home, coming inside Magnus with a grunt.

But the thing about the alien hormones was that it left them still hard after two or even three orgasms; Alec wasn't even close to done yet. Alec closed his eyes, trying to catch his breath, but the tight grip of Magnus' body around his hard cock felt too good. He opened his eyes to take in the sight of Magnus' muscles bunching and flexing as he struggled to get enough leverage to grind himself on Alec's cock, and Alec knew from personal experience that his knot was now pressing into Magnus' prostate. 

"Alexander... please, just let me come," Magnus moaned. His arms and legs were straining against the tentacles holding him as if he'd completely forgotten how to make them let go now that he was at the brink of orgasm, and Alec could see a knot swelling at the base of Magnus' cock. 

Alec wrapped one hand around the knot of Magnus' cock and use the other hand to jerk him off, fast and hard. Magnus let out a sharp cry and started coming, his release spilling all over Alec's fist and his body clenching down on Alec's cock inside him, but Alec kept going even after Magnus had finished coming. Magnus moaned, trying to pull away, but Alec's knot lodged inside his body kept him impaled on Alec's cock, and he was too fucked out to control his tentacles, leaving him helplessly bound and at Alec's mercy. Alec could feel Magnus' knot swelling in the grip of his fist, and Magnus' body pulsing and clenching around his cock was sending them both hurtling towards a second orgasm.

The second one hit a little harder than the first, and they were both panting at the end of it. Alec's stomach was a mess of come, Magnus' tentacles were still inside him, and the insides of Magnus' body was so slick with Alec's come that even with his knot engaged Alec could fuck Magnus shallowly.

"I can't, Alexander, _please_," Magnus whimpered, writhing desperately as Alec started stroking his cock again.

"One more, for me," Alec said firmly, his hand picking up speed as he thrust into Magnus. "Come for me, Magnus."

"I can't, it's too much. _Alexander!_" Magnus cried out as he came again, body clamping down so tight around Alec's cock that Alec followed him right over the edge as well.

\--

By the time they woke up, the rain had stopped. Alec smoothed a hand over Magnus' back, the skin smooth and normal again. His knot had gone down a while ago, allowing them to separate so Magnus could lie next to him, and they were both pleasantly sated and boneless. 

"Hey," Alec said, kissing Magnus on the forehead as he stirred in his arms. "We should probably be getting back to the ship before they get worried." 

Magnus hummed in agreement and tilted his face up so he could kiss Alec properly. "I'm surprised they haven't come looking for us, to be honest. My communicator hasn't gone off either."

"Oh. Um... that's probably because they didn't want to play third wheel. They think this is a date," Alec confessed. 

Magnus laughed lightly. "I wondered if that was your intention at first, but I didn't want to assume anything."

"I was going to plan a proper date. Not this," Alec assured him quickly.

"There's no hurry. And it doesn't have to be anything fancy - I'm sure we'll have fun, whatever it is. After all, a date is just an opportunity to get to know each other better," Magnus said. "Besides, I still want to find the cure to our little problem."

"You don't have to do that alone, you know. I mean, you can test the stuff on me too," Alec said. 

"Even if it involves tentacles?" Magnus asked. 

Alec shrugged. "Tentacles aren't so bad. Might be interesting to find out how it feels to have them."

Magnus smiled. "For science?" he asked teasingly. 

"For science," Alec agreed. 


End file.
